Field
The present disclosure relates to a liquid crystal display device and more particularly, to a liquid crystal display device which is improved in color display quality by minimizing a difference in response speed between sub-pixels.
Description of the Related Art
A liquid crystal display device is a display device including a liquid crystal layer. The liquid crystal display device is driven by adjusting a transmittance of light from a light source such as a backlight unit. In recent years, a demand for a liquid crystal display device with high resolution and low power consumption has increased.
The liquid crystal display device includes a plurality of pixels and a plurality of pixel electrodes configured to drive the plurality of pixels. If a pixel driving voltage is applied to the pixel electrodes, liquid crystal molecules in the liquid crystal layer are rotated due to a voltage difference between the pixel driving voltage and a common voltage applied to a common electrode. The amount of light to be transmitted is changed according to the degree of rotation of the liquid crystal molecules, and, thus, an image is displayed. In this regard, the pixel electrodes may be arrayed in various patterns, and an array pattern may affect the characteristics of the liquid crystal display device.
FIG. 1A is a plane view provided to explain a conventional liquid crystal display device. FIG. 1A illustrates components within a pixel including a red sub-pixel R, a green sub-pixel G, and a blue sub-pixel B. Referring to FIG. 1A, the conventional liquid crystal display device includes a data line 10, a gate line 20, a gate electrode 30, a source electrode 40, a drain electrode 50, and a pixel electrode 60R in the exemplary red sub-pixel R. The data line 10 transfers a data signal, and the gate line 20 transfers a scan signal for operating a thin film transistor. A channel is formed between the source electrode 40 and the drain electrode 50 and transfers the data signal to the pixel electrode 60R connected to the drain electrode 50 through a hole H in response to the scan signal.
The pixel electrode 60R is divided into three parts from a portion connected to the drain electrode 50 and extended as being tilted at a certain angle. Further, the pixel electrode 60R divided into three parts is titled again in a symmetrical direction and electrically connected. Thus, the pixel electrode 60R is not formed into a straight line, but tilted and extended. In the conventional liquid crystal display device, pixel electrodes 60R, 60G, and 60B on the respective sub-pixels R, G, and B have the same tilt angle. In other words, the pixel electrodes 60R, 60G, and 60B disposed on the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B, respectively, have the same shape with substantially the same tilt angle.
FIG. 1B is a table provided to explain a liquid crystal rotation time in the conventional liquid crystal display device. The table in FIG. 1B shows rotation times of liquid crystals when a voltage for displaying a specific gray scale is shifted to a voltage for displaying another specific gray scale. Herein, gray scales on the X-axis are initial gray scales, and gray scales on the Y-axis are changed gray scales. Values in the table represent the time required for a change from an initial gray scale to a changed gray scale.
Referring to FIG. 1B, in the conventional liquid crystal display device, it takes 13.3 μs for a change from an initial gray scale G0, i.e., black gray scale, to a gray scale G255. Further, it takes 23.7 μs for a change from the initial gray scale G0 to a gray scale G191 and 27.8 μs for a change from the initial gray scale G0 to a gray scale G63. As a difference in gray scale is increased, a difference in data voltage to be applied is increased and thus liquid crystals can be rotated at a higher speed. In a liquid crystal display device, at least three sub-pixels are disposed in one pixel, and the three sub-pixels can be controlled to respectively display different gray scales. Further, when a gray scale of a pixel is changed, a liquid crystal rotation time may affect a color display quality.
In order to inspect a color display quality of a liquid crystal display device, various methods may be used. For example, there may be used a method of applying a specific pattern to pixels and inspecting whether a desired color can be recognized without incongruity. FIG. 1C provides schematic diagrams to explain a change of pixels in the conventional liquid crystal display device.
(a) of FIG. 1C illustrates a plurality of exemplary pixels, and illustrates pixels PXL1 of a specific color with an RGB value of, e.g., (255, 191, 63) and pixels PXL2 in black state with an RGB value of, e.g., (0, 0, 0). Herein, a pattern that enables the pixels PXL2 in black state to have the color with the RGB value (255, 191, 63) may be applied.
Desirably, the pixels PXL2 need to be immediately changed to pixels of the color with the RGB value (255, 191, 63). However, as described above with reference to FIG. 1B, a liquid crystal rotation time is different in each sub-pixel. Therefore, a specific color is displayed first. In FIG. 1B, “Rrising” denotes a time required for a rotation of liquid crystals in a red sub-pixel, and the time is about 13 μs. Further, “Grising” which denotes a time required for a rotation of liquid crystals in a green sub-pixel is about 23 μs, and “Brising” which denotes a time required for a rotation of liquid crystals in a blue sub-pixel is about 27 μs. Accordingly, referring to (b) of FIG. 1C, only the red sub-pixel transmits a red light during a period between 13 μs and 23 μs. Referring to (c) of FIG. 1C, after about 24 μs, all the liquid crystals in the blue sub-pixel and the green sub-pixel are rotated, and, thus, a desired color can be recognized.
About 14 μs is a short period of time, but a time difference of about 8 μs or more can be recognized by the human eye. Therefore, if pixels are changed from a black state to a color having a specific gray scale, a color for liquid crystals rotated first is recognized first. If such a change in gray scale continuously occurs, tailing occurs.